This invention relates to doctor blades used with a tissuemaking, papermaking, or boardmaking machine, and to systems for minimizing doctor blade inventory associated with a tissuemaking, papermaking or boardmaking machine.
Doctor blades are used throughout a papermaking machine. Sometimes doctor blades are used to clean the surface of a roll used within a papermaking machine, for example press rolls, drying cylinders, and idler rolls. Doctor blades also function to prevent the paper web from becoming wrapped around a roll surface over which the paper web makes direct contact. Doctor blades function during a web break to remove broke from the surface of a roll and direct the broke into a broke pit for recycling. Doctor blades are also used to crepe a paper web and remove it from a Yankee dryer roll. In the past doctor blades of different materials have been used in different locations within a papermaking machine. The environment and conditions to which a doctor blade is subject depends dramatically on where the doctor blade is used in the papermaking machine. In the wet end, doctor blades may be subjected to corrosive effects due to chemicals dissolved or suspended in the white water. In the dry end a doctor blade may be subject to high temperatures associated with the drying process. In other locations wear may be a concern.
Doctor blades used in different parts of a papermaking machine are typically also of different lengths in the cross machine direction. The doctor blades differ in the length because as the paper web travels through the papermaking machine the paper shrinks in the cross machine direction and the edges are trimmed away such that the width of the paper web in the cross machine direction decreases as the paper web approaches the reel-up at the end of the papermaking machine. In addition, within a single papermaking plant there may be a number of different papermaking machines which have different widths. Moreover, the one plant may also include paper converting machinery such as slitters which create and handle paper which is substantially narrower than the width at which the paper web is manufactured.
Doctor blade material can be suppled to the paper mill as a blade cut to a particular length or as a coil of blade material which may be used as one continuous blade or as a series of identical blades which can be broken apart at labels positioned along the coil, the labels on the reel of blade material typically indicating the blade type and number of blades remaining in the coil. If a blade coil is used it may be packaged as shown is U.S. Pat. No. 6,068,272.
The combination of doctor blades of different material and different widths means that a papermaking machine requires a substantial inventory of different blade types and lengths. Depending on the application, a doctor blade may need to be changed as often as every day or as infrequently as once a year. If a proper doctor blade is not available the papermaking machine is not operated. To be sure the papermaking machine is not out of production for want of the necessary doctor blades, a relatively large inventory of doctor blades must be maintained. Because of the very high cost associated with keeping a papermaking machine out of production, the blade inventory system must err on the side of having too many, rather than too few, blades in the inventory. If the number of different doctor blades which are needed for a particular papermaking machine could be reduced, a substantial cost savings could be effected.
New doctor blade materials such as fiber reinforcement vinylesterurethanes or polyether amides may allow doctor blades constructed of the same material to be used in multiple locations throughout a papermaking machine, however this will not substantially reduce doctor blade inventory unless a way can be found to use identical doctor blades throughout a papermaking machine.